1. Field of the Invention
This invention relates to a keyboard unit having a plurality of key switches, and in particular to a thin keyboard unit which is applied, for instance, to a note type personal computer.
2. Description of the Prior Art
A cross link type key switch, as shown in FIGS. 10 and 11, has been disclosed by Japanese Patent Kokai Publication No. 342943/1993.
In the key switch, a key top holder 25 is formed with the outer legs 29 and inner legs 32 of link members 26 and 27 which are coupled to one another in such a manner that the cross angle therebetween changes freely according to the height of a key top, and the engaging protrusions 29a and 32a of those legs 29 and 32 are engaged with engaging recesses 22b and 22c formed in the housing 22, respectively.
The key top holder 25 has an operating piece 30 which elastically abuts against an elastic member 24, whereby a membrane switch 16 is operated by the elastic member 24 as the key top 23 is moved up and down.
The above-described key switch suffers from the following difficulties:
The key switch requires, in addition to a supporting board 15 placed below the membrane switch 16 for supporting the latter 16, the housing 22 above the membrane switch 16 for engagement with the key top holder 25 through the engaging recesses 22b and 22c of the housing 22. Hence, the thickness of the housing 22 makes it difficult to decrease the thickness of the entire key switch.
Further, since, as was described above, the key switch is designed such that the operating piece 30 provided in the key top holder 25 elastically abuts against the elastic member 24, the thickness of the operating piece 30 also makes it difficult to decrease the thickness of the key switch.
Furthermore, since the operating piece 30 provided in the key top holder 25 elastically abuts against the elastic member 24 adapted to drive the membrane switch 26, the clicking feeling which is caused due to deformation of the elastic member 24 when the operator taps the key top 23 is hardly transmitted to the operator.
In the keyboard unit, the elastic member 24 is assembled in each of the key switches. Hence, the assembling work is rather troublesome, and sometimes it may be forgot to assemble the elastic member 24 in the key switch. Thus, the keyboard unit is relatively high in manufacturing cost.
On the other hand, there is a demand for reduction of the number of parts of the keyboard unit, to decrease the part cost and the part managing manhour.
Moreover, in order to prevent the permanent set in fatigue of the elastic member in the key switch, it is necessary to increase the size of the elastic member as much as possible.
In a key switch in which its key top is large in area with respect to the elastic member, an interlocking bar which is a substantially U-shaped metal wire is employed to smoothly operate the key switch. However, the key switch is disadvantageous in that its assembling work is intricate, and the manufacturing cost is accordingly high.